Java HotSpot Virtual Machine

Here's my HelloWorld.java

public class HelloWorld 
{
	  public native void displayMessage();
	  static 
	  {
	    System.loadLibrary("libhelloworld2"); 
	  }
}

Here's main Main.java

public class Main 
{
	  public static void main(String[] args) 
	  {
	    HelloWorld hello = new HelloWorld();
	    hello.displayMessage();
	  }
}

Here's my HelloWorld.h

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class HelloWorld */

#ifndef _Included_HelloWorld
#define _Included_HelloWorld
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     HelloWorld
 * Method:    displayMessage
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_HelloWorld_displayMessage
  (JNIEnv *, jobject);

#ifdef __cplusplus
}
#endif
#endif

Here's my HelloWorld.cpp

/*
 * HelloWorld.cpp
 *
 *  Created on: Jul 11, 2008
 *      Author: panderson
 */

#include <stdio.h>
#include "HelloWorld.h"   // this header file was generated by javah
JNIEXPORT void JNICALL Java_HelloWorld_displayMessage(JNIEnv *env, jobject obj)
{
  printf("Hello World!\n");
}

Here's the output that I get when I run it

Exception in thread "main" java.lang.UnsatisfiedLinkError: displayMessage
	at HelloWorld.displayMessage(Native Method)
	at Main.main(Main.java:7)

I'm pretty sure it is finding the DLL file because when it does not find the DLL the error message is as follows

Exception in thread "main" java.lang.UnsatisfiedLinkError: no libhelloworld2 in java.library.path
	at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1682)
	at java.lang.Runtime.loadLibrary0(Runtime.java:822)
	at java.lang.System.loadLibrary(System.java:993)
	at HelloWorld.<clinit>(HelloWorld.java:7)
	at Main.main(Main.java:6)

------------------------------------------------------------------

So it seems to be loading the DLL but when it goes to call the method it generates an exception instead.

I used MinGW (g++) to create the DLL. Here's the compilation instructions it generated to create the DLL

**** Build of configuration Debug for project helloworld2 ****

**** Internal Builder is used for build               ****
g++ -IC:\Java\jdk1.5\include -IC:\Java\jdk1.5\include\win32 -O0 -g3 -Wall -c -fmessage-length=0 -oHelloWorld.o ..\HelloWorld.cpp
g++ -shared -olibhelloworld2.dll HelloWorld.o
Build complete for project helloworld2
Time consumed: 280  ms.  

So I am stumped as to why it is generating the exception. It's a real show stopper.

Any help would be greatly appreciated, thanks.

- Perry

Edited by: perriera on Jul 11, 2008 11:56 AM